The phosphatidylinositol 3-kinase/Akt signaling pathway modulates the endocrine differentiation of trophoblast cells

Hypothalamus Transcriptome Reveals Key lncRNAs and mRNAs Associated with Fecundity in Goats

The hypothalamus (hyp) serves as the regulatory hub of the neuroendocrine system, synthesizing and secreting reproductive hormones that modulate estrus, follicular maturation, and embryonic development in goats. This study employed RNA-seq analysis to examine gene expression in the hypothalamic tissue of Yunshang black goats during the luteal phase in goats with high fecundity (LP_HY), during the luteal phase in goats with low fecundity (LP_LY), during the follicular phase in goats with high fecundity (FP_HY), and during the follicular phase in goats with low fecundity (FP_LY). Differential long non-coding RNAs (DE lncRNAs) and differential mRNAs (DE mRNAs) were subjected to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses and the construction of co-expression networks associated with reproduction. As a result, DE lncRNAs (390, 375, 405, and 394) and DE mRNAs (1836, 2047, 2003, and 1963) were identified in the four comparisons, namely FP_LY vs. FP_HY, LP_HY vs. FP_HY, LP_LY vs. FP_LY, and LP_LY vs. LP_HY, respectively. Functional annotations indicated significant enrichment of numerous DE lncRNAs and DE mRNAs in reproduction-related pathways such as the gonadotropin-releasing hormone pathway, the prolactin signaling pathway, the estrogen signaling pathway, the Wnt signaling pathway, oocyte meiosis, and progesterone-mediated oocyte maturation. The co-expression network of lncRNAs and target genes identified the interrelationships between reproduction-related genes such as IGF1, PORCN, PLCB2, MAPK8, PRLR, and CPEB2 with our newly discovered lncRNAs. This study expands the understanding of lncRNAs and mRNAs in goat hypothalamic tissue and provides new insights into molecular mechanisms related to goat reproduction.

The Expression Pattern and Functional Analysis of Extracellular Vesicle Long Non-Coding RNAs from Uterine Fluid During Implantation in Pig

Long non-coding RNAs (lncRNAs) act as competing endogenous RNAs and play significant roles in porcine embryo development. Extracellular vesicles (EVs) in the uterine fluid (UF) can target and deliver maternal endometrial signalling molecules to embryonic trophoblast cells, exerting crucial regulatory effects during embryo implantation. However, the specific roles of lncRNAs carried by UF-EVs during the embryo implantation period have not been thoroughly reported in the literature. In the present study, high-throughput sequencing and biological tools were applied to analyse lncRNAs in UF-EVs on days 9, 12, and 15 of pregnancy to identify key regulatory lncRNAs in UF-EVs during the porcine embryonic implantation period and to explore their expression patterns and functional roles. A total of 30,203 lncRNAs were identified and 7879 differentially expressed lncRNAs were screened, and qRT-PCR was used to verify the sequencing data. Days 9-12 of pregnancy represent a critical stage of embryo implantation characterised by substantial morphological changes in porcine embryos. During this period, we identified a total of 4348 differentially expressed lncRNAs. Through screening and validation, we discovered that LNC_026212 was highly expressed on day 12 of pregnancy and can promote the proliferation and migration of porcine trophoblast cells (PTr cells). These novel findings contribute to our understanding of the impact of lncRNAs on porcine reproductive processes, offering new research directions to improve the success rate of embryo implantation in pigs.

The interaction of ER stress and autophagy in trophoblasts: navigating pregnancy outcome†

The endoplasmic reticulum is a complex and dynamic organelle that initiates unfolded protein response and endoplasmic reticulum stress in response to the accumulation of unfolded or misfolded proteins within its lumen. Autophagy is a paramount intracellular degradation system that facilitates the transportation of proteins, cytoplasmic components, and organelles to lysosomes for degradation and recycling. Preeclampsia and intrauterine growth retardation are two common complications of pregnancy associated with abnormal trophoblast differentiation and placental dysfunctions and have a major impact on fetal development and maternal health. The intricate interplay between endoplasmic reticulum stress, and autophagy and their impact on pregnancy outcomes, through mediating trophoblast differentiation and placental development, has been highlighted in various reports. Autophagy controls trophoblast regulation through a variety of gene expressions and signaling pathways while excessive endoplasmic reticulum stress triggers downstream apoptotic signaling, culminating in trophoblast apoptosis. This comprehensive review delves into the intricacies of placental development and explores the underlying mechanisms of preeclampsia and intrauterine growth retardation. In addition, this review will elucidate the molecular mechanisms of endoplasmic reticulum stress and autophagy, both individually and in their interplay, in mediating placental development and trophoblast differentiation, particularly highlighting their roles in preeclampsia and intrauterine growth retardation development. This research seeks to the interplay between endoplasmic reticulum stress and impaired autophagy in the placental trophoderm, offering novel insights into their contribution to pregnancy complications.

Trophoblast Differentiation: Mechanisms and Implications for Pregnancy Complications

Placental development is a tightly controlled event, in which cell expansion from the trophectoderm occurs in a spatiotemporal manner. Proper trophoblast differentiation is crucial to the vitality of this gestational organ. Obstructions to its development can lead to pregnancy complications, such as preeclampsia, fetal growth restriction, and preterm birth, posing severe health risks to both the mother and offspring. Currently, the only known treatment strategy for these complications is delivery, making it an important area of research. The aim of this review was to summarize the known information on the development and mechanistic regulation of trophoblast differentiation and highlight the similarities in these processes between the human and mouse placenta. Additionally, the known biomarkers for each cell type were compiled to aid in the analysis of sequencing technologies.

The AKT1-FOXO4 axis reciprocally regulates hemochorial placentation

Hemochorial placentation involves the differentiation of invasive trophoblast cells, specialized cells that possess the capacity to exit the placenta and invade into the uterus where they restructure the vasculature. Invasive trophoblast cells arise from a well-defined compartment within the placenta, referred to as the junctional zone in rat and the extravillous trophoblast cell column in human. In this study, we investigated roles for AKT1, a serine/threonine kinase, in placental development using a genome-edited/loss-of-function rat model. Disruption of AKT1 resulted in placental, fetal and postnatal growth restriction. Forkhead box O4 (Foxo4), which encodes a transcription factor and known AKT substrate, was abundantly expressed in the junctional zone and in invasive trophoblast cells of the rat placentation site. Foxo4 gene disruption using genome editing resulted in placentomegaly, including an enlarged junctional zone. AKT1 and FOXO4 regulate the expression of many of the same transcripts expressed by trophoblast cells, but in opposite directions. In summary, we have identified AKT1 and FOXO4 as part of a regulatory network that reciprocally controls critical indices of hemochorial placenta development.

SUV39H2 controls trophoblast stem cell fate

BACKGROUND

The placenta is formed by the coordinated expansion and differentiation of trophoblast stem (TS) cells along a multi-lineage pathway. Dynamic regulation of histone 3 lysine 9 (H3K9) methylation is pivotal to cell differentiation for many cell lineages, but little is known about its involvement in trophoblast cell development.

METHODS

Expression of H3K9 methyltransferases was surveyed in rat TS cells maintained in the stem state and following differentiation. The role of suppressor of variegation 3-9 homolog 2 (SUV39H2) in the regulation of trophoblast cell lineage development was investigated using a loss-of-function approach in rat TS cells and ex vivo cultured rat blastocysts.

RESULTS

Among the twelve-known H3K9 methyltransferases, only SUV39H2 exhibited robust differential expression in stem versus differentiated TS cells. SUV39H2 transcript and protein expression were high in the stem state and declined as TS cells differentiated. Disruption of SUV39H2 expression in TS cells led to an arrest in TS cell proliferation and activation of trophoblast cell differentiation. SUV39H2 regulated H3K9 methylation status at loci exhibiting differentiation-dependent gene expression. Analyses of SUV39H2 on ex vivo rat blastocyst development supported its role in regulating TS cell expansion and differentiation. We further identified SUV39H2 as a downstream target of caudal type homeobox 2, a master regulator of trophoblast lineage development.

CONCLUSIONS

Our findings indicate that SUV39H2 contributes to the maintenance of TS cells and restrains trophoblast cell differentiation.

GENERAL SIGNIFICANCE

SUV39H2 serves as a contributor to the epigenetic regulation of hemochorial placental development.

Histone demethylase JMJD2B/KDM4B regulates transcriptional program via distinctive epigenetic targets and protein interactors for the maintenance of trophoblast stem cells

Trophoblast stem cell (TSC) is crucial to the formation of placenta in mammals. Histone demethylase JMJD2 (also known as KDM4) family proteins have been previously shown to support self-renewal and differentiation of stem cells. However, their roles in the context of the trophoblast lineage remain unclear. Here, we find that knockdown of Jmjd2b resulted in differentiation of TSCs, suggesting an indispensable role of JMJD2B/KDM4B in maintaining the stemness. Through the integration of transcriptome and ChIP-seq profiling data, we show that JMJD2B is associated with a loss of H3K36me3 in a subset of embryonic lineage genes which are marked by H3K9me3 for stable repression. By characterizing the JMJD2B binding motifs and other transcription factor binding datasets, we discover that JMJD2B forms a protein complex with AP-2 family transcription factor TFAP2C and histone demethylase LSD1. The JMJD2B-TFAP2C-LSD1 complex predominantly occupies active gene promoters, whereas the TFAP2C-LSD1 complex is located at putative enhancers, suggesting that these proteins mediate enhancer-promoter interaction for gene regulation. We conclude that JMJD2B is vital to the TSC transcriptional program and safeguards the trophoblast cell fate via distinctive protein interactors and epigenetic targets.

CXCR4 signaling at the fetal-maternal interface may drive inflammation and syncytia formation during ovine pregnancy†

Early pregnancy features complex signaling between fetal trophoblast cells and maternal endometrium directing major peri-implantation events including localized inflammation and remodeling to establish proper placental development. Proinflammatory mediators are important for conceptus attachment, but a more precise understanding of molecular pathways regulating this process is needed to understand how the endometrium becomes receptive to implantation. Both chemokine ligand 12 (CXCL12) and its receptor CXCR4 are expressed by fetal and maternal tissues. We identified this pair as a critical driver of placental angiogenesis, but their additional importance to inflammation and trophoblast cell survival, proliferation, and invasion imply a role in syncytia formation at the fetal-maternal microenvironment. We hypothesized that CXCL12 encourages both endometrial inflammation and conceptus attachment during implantation. We employed separate ovine studies to (1) characterize endometrial inflammation during early gestation in the ewe, and (2) establish functional implications of CXCL12 at the fetal-maternal interface through targeted intrauterine infusion of the CXCR4 inhibitor AMD3100. Endometrial tissues were evaluated for inflammatory mediators, intracellular signaling events, endometrial modifications, and trophoblast syncytialization using western blotting and immunohistochemistry. Endometrial tissue from ewes receiving CXCR4 inhibitor demonstrated dysregulated inflammation and reduced AKT and NFKB, paired with elevated autophagic activity compared to control. Immunohistochemical observation revealed an impairment in endometrial surface remodeling and diminished trophoblast syncytialization following localized CXCR4 inhibition. These data suggest CXCL12-CXCR4 regulates endometrial inflammation and remodeling for embryonic implantation, and provide insight regarding mechanisms that, when dysregulated, lead to pregnancy pathologies such as intrauterine growth restriction and preeclampsia.

Hemochorial placentation: development, function, and adaptations

Placentation is a reproductive adaptation that permits fetal growth and development within the protected confines of the female reproductive tract. Through this important role, the placenta also determines postnatal health and susceptibility to disease. The hemochorial placenta is a prominent feature in primate and rodent development. This manuscript provides an overview of the basics of hemochorial placental development and function, provides perspectives on major discoveries that have shaped placental research, and thoughts on strategies for future investigation.

Autophagy in the placenta

Autophagy is an evolutionarily conserved catalytic process by which cytoplasmic components including damaged macromolecules and organelles are degraded. The role of autophagy includes adaptive responses to nutrition deprivation or intracellular stimuli. Although autophagosomes were first observed in early 1960s, it was 1990s that autophagy-related genes in yeast were identified and studied. Nowadays, the molecular machinery of autophagy and signaling pathway to various stimuli are almost outlined. Dysregulation of autophagic activity has been implicated in many human diseases including neurodegenerative diseases, infection and inflammation, and malignancies. However, since current understanding of autophagy in placenta is just at the beginning, this paper aims to provide general information on autophagy (part I) and to summarize articles on autophagy in human placenta (part II). This review article will serve as a basis for further researches on autophagy in relation to human pregnancy and its complications.

Phosphoinositide 3-Kinase (PI3K) Subunit p110δ Is Essential for Trophoblast Cell Differentiation and Placental Development in Mouse

Maternal PI3K p110δ has been implicated in smaller litter sizes in mice, but its underlying mechanism remains unclear. The placenta is an indispensable chimeric organ that supports mammalian embryonic development. Using a mouse model of genetic inactivation of PI3K p110δ (p110δ^D910A/D910A), we show that fetuses carried by p110δ^D910A/D910A females were growth retarded and showed increased mortality in utero mainly during placentation. The placentas in p110δ^D910A/D910A females were anomalously anemic, exhibited thinner spongiotrophoblast layer and looser labyrinth zone, which indicate defective placental vasculogenesis. In addition, p110δ was detected in primary trophoblast giant cells (P-TGC) at early placentation. Maternal PI3K p110δ inactivation affected normal TGCs generation and expansion, impeded the branching of chorioallantoic placenta but enhanced the expression of matrix metalloproteinases (MMP-2, MMP-12). Poor vasculature support for the developing fetoplacental unit resulted in fetal death or gross growth retardation. These data, taken together, provide the first in vivo evidence that p110δ may play an important role in placental vascularization through manipulating trophoblast giant cell.

GW5074 and PP2 kinase inhibitors implicate nontraditional c-Raf and Lyn function as drivers of retinoic acid-induced maturation

The multivariate nature of cancer necessitates multi-targeted therapy, and kinase inhibitors account for a vast majority of approved cancer therapeutics. While acute promyelocytic leukemia (APL) patients are highly responsive to retinoic acid (RA) therapy, kinase inhibitors have been gaining momentum as co-treatments with RA for non-APL acute myeloid leukemia (AML) differentiation therapies, especially as a means to treat relapsed or refractory AML patients. In this study GW5074 (a c-Raf inhibitor) and PP2 (a Src-family kinase inhibitor) enhanced RA-induced maturation of t(15;17)-negative myeloblastic leukemia cells and rescued response in RA-resistant cells. PD98059 (a MEK inhibitor) and Akti-1/2 (an Akt inhibitor) were less effective, but did tend to promote maturation-uncoupled G1/G0 arrest, while wortmannin (a PI3K inhibitor) did not enhance differentiation surface marker expression or growth arrest. PD98059 and Akti-1/2 did not enhance differentiation markers and have potential, antagonistic off-targets effects on the aryl hydrocarbon receptor (AhR), but neither could the AhR agonist 6-formylindolo(3,2-b)carbazole (FICZ) rescue differentiation events in the RA-resistant cells. GW5074 rescued early CD38 expression in RA-resistant cells exhibiting an early block in differentiation before CD38 expression, while for RA-resistant cells with differentiation blocked later, PP2 rescued the later differentiation marker CD11b; but surprisingly, the combination of the two was not synergistic. Kinases c-Raf, Src-family kinases Lyn and Fgr, and PI3K display highly correlated signaling changes during RA treatment, while activation of traditional downstream targets (Akt, MEK/ERK), and even the surface marker CD38, were poorly correlated with c-Raf or Lyn during differentiation. This suggests that an interrelated kinase module involving c-Raf, PI3K, Lyn and perhaps Fgr functions in a nontraditional way during RA-induced maturation or during rescue of RA induction therapy using inhibitor co-treatment in RA-resistant leukemia cells.

Adaptive mechanisms controlling uterine spiral artery remodeling during the establishment of pregnancy

Implantation of the embryo into the uterus triggers the initiation of hemochorial placentation. The hemochorial placenta facilitates the acquisition of maternal resources required for embryo/fetal growth. Uterine spiral arteries form the nutrient supply line for the placenta and fetus. This vascular conduit undergoes gestation stage-specific remodeling directed by maternal natural killer cells and embryo-derived invasive trophoblast lineages. The placentation site, including remodeling of the uterine spiral arteries, is shaped by environmental challenges. In this review, we discuss the cellular participants controlling pregnancy-dependent uterine spiral artery remodeling and mechanisms responsible for their development and function.

The role of autophagy in the placenta as a regulator of cell death

The placenta is a temporary fetomaternal organ capable of supporting fetal growth and development during pregnancy. In particular, abnormal development and dysfunction of the placenta due to cha nges in the proliferation, differentiation, cell death, and invasion of trophoblasts induce several gynecological diseases as well as abnormal fetal development. Autophagy is a catalytic process that maintains cellular structures by recycling building blocks derived from damaged microorganelles or proteins resulting from digestion in lysosomes. Additionally, autophagy is necessary to maintain homeostasis during cellular growth, development, and differentiation, and to protect cells from nutritional deficiencies or factors related to metabolism inhibition. Induced autophagy by various environmental factors has a dual role: it facilitates cellular survival in normal conditions, but the cascade of cellular death is accelerated by over-activated autophagy. Therefore, cellular death by autophagy has been known as programmed cell death type II. Autophagy causes or inhibits cellular death via the other mechanism, apoptosis, which is programmed cell death type I. Recently, it has been reported that autophagy increases in placenta-related obstetrical diseases such as preeclampsia and intrauterine growth retardation, although the mechanisms are still unclear. In particular, abnormal autophagic mechanisms prevent trophoblast invasion and inhibit trophoblast functions. Therefore, the objectives of this review are to examine the characteristics and functions of autophagy and to investigate the role of autophagy in the placenta and the trophoblast as a regulator of cell death.

First-trimester euploid miscarriages analysed by array-CGH

It is estimated that 10-15 % of all clinically recognised pregnancies results in a miscarriage, most of which occur during the first trimester. Large-scale chromosomal abnormalities have been found in up to 50 % of first-trimester spontaneous abortions and, for several decades, standard cytogenetic analysis has been used for their identification. Recent studies have proven that array comparative genomic hybridisation (array-CGH) is a useful tool for the detection of genome imbalances in miscarriages, showing a higher resolution, a significantly higher detection rate and overcoming problems of culture failures, maternal contamination and poor chromosome morphology. In this study, we investigated the possibility that submicroscopic chromosomal changes, not detectable by conventional cytogenetic analysis, exist in euploid miscarriages and could be causative for the spontaneous abortion. We analysed with array-CGH technology 40 foetal tissue samples derived by first-trimester miscarriages with a normal karyotype. A whole-genome microarray with a 100-Kb resolution was used for the analysis. Forty-five copy number variants (CNVs), ranging in size between 120 Kb and 4.3 Mb, were identified in 31 samples (24 gains and 21 losses). Ten samples (10/31, 32 %) have more than one CNV. Thirty-one CNVs (68 %) were defined as common CNVs and 14 were classified as unique. Six genes and five microRNAs contained within these CNVs will be discussed. This study shows that array-CGH is useful for detecting submicroscopic CNVs and identifying candidate genes which could account for euploid miscarriages.

Embryonic stem cell-derived trophoblast differentiation: a comparative review of the biology, function, and signaling mechanisms

The development of the placenta is imperative for successful pregnancy establishment, yet the earliest differentiation events of the blastocyst-derived trophectoderm that forms the placenta remain difficult to study in humans. Human embryonic stem cells (hESC) display a unique ability to form trophoblast cells when induced to differentiate either by the addition of exogenous BMP4 or by the formation of cellular aggregates called embryoid bodies. While mouse trophoblast stem cells (TSC) have been isolated from blastocyst outgrowths, mouse ESC do not spontaneously differentiate into trophoblast cells. In this review, we focus on addressing the similarities and differences between mouse TSC differentiation and hESC-derived trophoblast differentiation. We discuss the functional and mechanistic diversity that is found in different species models. Of central importance are the unique signaling events that trigger downstream gene expression that create specific cellular fate decisions. We support the idea that we must understand the nuances that hESC differentiation models display so that investigators can choose the appropriate model system to fit experimental needs.

Regulatory pathways controlling the endovascular invasive trophoblast cell lineage

Hemochorial placentation is characterized by trophoblast-directed uterine spiral artery remodeling. The rat and human both possess hemochorial placentation and exhibit remarkable similarities regarding the depth of trophoblast invasion and the extent of uterine vascular modification. In vitro and in vivo research methodologies have been established using the rat as an animal model to investigate the extravillous/invasive trophoblast lineage. With these research approaches, two signaling pathways controlling the differentiation and invasion of the trophoblast cell lineage have been identified: i) hypoxia/hypoxia inducible factor and ii) phosphatidylinositol 3-kinase/AKT/Fos like antigen 1. Dissection of these pathways has facilitated identification of fundamental regulators of the invasive trophoblast cell lineage.

The maternally expressed gene Tssc3 regulates the expression of MASH2 transcription factor in mouse trophoblast stem cells through the AKT-Sp1 signaling pathway

Tssc3 is a maternally expressed/paternally silenced imprinted gene. Recent evidence suggests that the loss of TSSC3 results in placental overgrowth in mice. These findings showed that the TSSC3 gene functions as a negative regulator of placental growth. In this study, we describe the function of TSSC3 and its signaling pathway in mouse trophoblast stem (TS) cell differentiation. First of all, we tested Tssc3 expression levels in TS cells. TS cells expressed Tssc3, and its expression level was the highest from day 1 to 4 but was down-regulated at day 5 after the induction of differentiation. Overexpression of TSSC3 in TS cells up-regulated Gcm1 and Mash2, which are marker genes of mouse trophoblast differentiation. Down-regulation of TSSC3 by siRNA enhanced Pl1 and Tpbpa expression in TS cells cultured under stem cell conditions, suggesting the contribution of TSSC3 to the differentiation from TS to trophoblast progenitors and/or labyrinth trophoblasts. TSSC3 activated the PI3K/AKT pathway through binding with phosphatidylinositol phosphate lipids and enhanced the activity of a promoter containing an E-box structure, which is the binding sequence of the Mash2 downstream target gene promoter. PI3K inhibitor suppressed the promoter activity induced by TSSC3. TSSC3 induced Sp1 translocation from cytoplasm to nucleus through the PI3K/AKT pathway. Nuclear Sp1 activated the Mash2 transcription by Sp1 binding with a consensus Sp1-binding motif. This is the first report describing that TSSC3 plays an important role in the differentiation from TS to trophoblast progenitors and/or labyrinth trophoblasts through the TSSC3/PI3K/AKT/MASH2 signaling pathway.

Akt1 and insulin-like growth factor 2 (Igf2) regulate placentation and fetal/postnatal development

Phenotypic characterization of Akt1 and Igf2 null mice has revealed roles for each in the regulation of placentation, and fetal and postnatal growth. Insulin-like growth factor 2 (IGF2) is encoded by the Igf2 gene and influences cellular function, at least in part, through activation of an intracellular serine/threonine kinase called AKT1. Akt1 and Igf2 null mice were originally characterized on inbred and mixed genetic backgrounds, prohibiting direct comparisons of their phenotypes. The impact of loss of AKT1 or IGF2 on placental, fetal, and postnatal function were examined following transfer of Akt1 and Igf2 null mutations to an outbred CD1 genetic background. Disruption of IGF2 did not affect AKT expression or activation. Both Akt1-/- and Igf2-/- mice exhibited decreased placental weight, fetal weight and viability. Deregulation of placental growth was similar in Akt1 and Igf2 nulls; however, disruption of Igf2 had a more severe impact on prenatal survival and postnatal growth. Placental structure, including organization of junctional and labyrinth zones and development of the interstitial, invasive, trophoblast lineage, were similar in mutant and wild-type mice. Akt1 and Igf2 null mutations affected postnatal growth. The relative impact of each gene differed during pre-weaning versus post-weaning growth phases. AKT1 had a more significant role during pre-weaning growth, whereas IGF2 was a bigger contributor to post-weaning growth. Akt1 and Igf2 null mutations impact placental, fetal and postnatal growth. Placental phenotypes are similar; however, fetal and postnatal growth patterns are unique to each mutation.

N-carbamylglutamate enhances pregnancy outcome in rats through activation of the PI3K/PKB/mTOR signaling pathway

Administration of N-carbamylglutamate (NCG), an analogue of endogenous N-acetyl-glutamate (an activator of arginine synthesis) has been shown to enhance neonatal growth by increasing circulating arginine levels. However, the effect of NCG on pregnancy remains unknown. This study examined the effects of NCG on pregnancy outcome and evaluated potential mechanisms involved. Reproductive performance, embryo implantation, and concentration of amino acids in serum and uterine flushing, were determined in rats fed control or NCG supplemented diets. Ishikawa cells and JAR cells were used to examine the mechanism by which NCG affects embryo implantation. Dietary NCG supplementation increased serum levels of arginine, onithine, and proline, as well as uterine levels of arginine, glutamine, glutamate, and proline. Additionally, it stimulated LIF expression, and enhanced the activation of signal transduction and activator of transcription 3 (Stat3), protein kinase B (PKB), and 70-kDa ribosomal protein S6 kinase (S6K1) during the periimplantation period, resulting in an increase in litter size but not birth weight. In uterine Ishikawa cells, LIF expression was also enhanced by treatment with arginine and its metabolites. In trophoblast JAR cells, treatment with arginine and its metabolites enhanced Stat3, PKB, and S6K1 activation and facilitated cellular adhesion activity. These effects were abolished by pretreatment with inhibitors of phosphatidylinositol 3-kinase (wortmannin) and mammalian target of rapamycin (rapamycin). The results demonstrate that NCG supplementation enhances pregnancy outcome and have important implications for the pregnancy outcome of mammalian species.

Rat placentation: an experimental model for investigating the hemochorial maternal-fetal interface

The rat possesses hemochorial placentation with deep intrauterine trophoblast cell invasion and trophoblast-directed uterine spiral artery remodeling; features shared with human placentation. Recognition of these similarities spurred the establishment of in vitro and in vivo research methods using the rat as an animal model to address mechanistic questions regarding development of the hemochorial placenta. The purpose of this review is to provide the requisite background to help move the rat to the forefront in placentation research.

FOSL1 is integral to establishing the maternal-fetal interface

Remodeling of uterine spiral arteries by trophoblast cells is a requisite process for hemochorial placentation and successful pregnancy. The rat exhibits deep intrauterine trophoblast invasion and accompanying trophoblast-directed vascular modification. The involvement of phosphatidylinositol 3 kinase (PI3K), AKT, and Fos-like antigen 1 (FOSL1) in regulating invasive trophoblast and hemochorial placentation was investigated using Rcho-1 trophoblast stem cells and rat models. Disruption of PI3K/AKT with small-molecule inhibitors interfered with the differentiation-dependent elaboration of a signature invasive-vascular remodeling trophoblast gene expression profile and trophoblast invasion. AKT isoform-specific knockdown also affected the signature invasive-vascular remodeling trophoblast gene expression profile. Nuclear FOSL1 increased during trophoblast cell differentiation in a PI3K/AKT-dependent manner. Knockdown of FOSL1 disrupted the expression of a subset of genes associated with the invasive-vascular remodeling trophoblast phenotype, including the matrix metallopeptidase 9 gene (Mmp9). FOSL1 was shown to occupy regions of the Mmp9 promoter in trophoblast cells critical for the regulation of Mmp9 gene expression. Inhibition of FOSL1 expression also abrogated trophoblast invasion, as assessed in vitro and following in vivo trophoblast-specific lentivirally delivered FOSL1 short hairpin RNA (shRNA). In summary, FOSL1 is a key downstream effector of the PI3K/AKT signaling pathway responsible for development of trophoblast lineages integral to establishing the maternal-fetal interface.

Interplay of cAMP and MAPK pathways in hCG secretion and fusogenic gene expression in a trophoblast cell line

Differentiation of human placental mononuclear trophoblasts into a multinucleate syncytium involves up-regulation of key proteins promoting cell fusion and increased capacity for placental hormonogenesis. It is well established that the activation of adenylyl cyclase leads to increased expression of trophoblast fusogenic gene machinery and human chorionic gonadotropin (hCG) secretion. We used the forskolin-induced syncytialisation of BeWo choriocarcinoma cells as a model to characterise in detail the signalling pathway downstream of adenylyl cyclase. Forskolin treatment induced a rapid and potent ERK1/2 and p38MAPK phosphorylation; this cascade required PKA-AKAP interactions and led to downstream CREB-1/ATF-1 phosphorylation via ERK1/2-dependent but p38MAPK-independent mechanisms. Interestingly both p38MAPK and ERK1/2 were involved in forskolin-induced hCG-secretion, suggesting the presence of additional p38MAPK-dependent but CREB-1/ATF-1-independent pathways. Forskolin treatment of BeWo cells significantly up-regulated the expression of various fusogenic gene mRNAs, including syncytin-1 and -2 (by 3- and 10-fold, respectively) the transcription factors old astrocyte specifically induced substance (OASIS) and glial cells missing a (GCMa) (by 3- and 6-fold, respectively) and the syncytin-2 receptor, major facilitator superfamily domain containing 2 (MFSD2) (by 2-fold). Up-regulation of AKAP79 and AKAP250 (by 2.5- and 4-fold, respectively) was also identified in forskolin-treated BeWo cells. Forskolin effects on all these genes were suppressed by chemical inhibition of p38MAPK whereas only specific genes were sensitive to ERK1/2 inhibition. This data provide novel insights into the signalling molecules and mechanisms regulating fusogenic gene expression by the adenylyl cyclase pathway.

Phosphatidylinositol 3 kinase modulation of trophoblast cell differentiation

BACKGROUND

The trophoblast lineage arises as the first differentiation event during embryogenesis. Trophoblast giant cells are one of several end-stage products of trophoblast cell differentiation in rodents. These cells are located at the maternal-fetal interface and are capable of invasive and endocrine functions, which are necessary for successful pregnancy. Rcho-1 trophoblast stem cells can be effectively used as a model for investigating trophoblast cell differentiation. In this report, we evaluated the role of the phosphatidylinositol 3-kinase (PI3K) signaling pathway in the regulation of trophoblast cell differentiation. Transcript profiles from trophoblast stem cells, differentiated trophoblast cells, and differentiated trophoblast cells following disruption of PI3K signaling were generated and characterized.

RESULTS

Prominent changes in gene expression accompanied the differentiation of trophoblast stem cells. PI3K modulated the expression of a subset of trophoblast cell differentiation-dependent genes. Among the PI3K-responsive genes were those encoding proteins contributing to the invasive and endocrine phenotypes of trophoblast giant cells.

CONCLUSIONS

Genes have been identified with differential expression patterns associated with trophoblast stem cells and trophoblast cell differentiation; a subset of these genes are regulated by PI3K signaling, including those impacting the differentiated trophoblast giant cell phenotype.

The STOX1 genotype associated with pre-eclampsia leads to a reduction of trophoblast invasion by alpha-T-catenin upregulation

By using complementary in vitro and ex vivo approaches, we show that the risk allele (Y153H) of the pre-eclampsia susceptibility gene STOX1 negatively regulates trophoblast invasion by upregulation of the cell-cell adhesion protein alpha-T-catenin (CTNNA3). This is effectuated at the crucial epithelial-mesenchymal transition of proliferative into invasive extravillous trophoblast. This STOX1-CTNNA3 interaction is direct and includes Akt-mediated phosphorylated control of nucleo-cytoplasmic shuttling and ubiquitin-mediated degradation as shared with the FOX multigene family. This, to our knowledge, is the first time a genotype associated with pre-eclampsia has been shown to directly limit first trimester extravillous trophoblast invasion, the earliest hallmark of pre-eclampsia.

Critical growth factors and signalling pathways controlling human trophoblast invasion

Invasion of placental trophoblasts into uterine tissue and vessels is an essential process of human pregnancy and fetal development. Due to their remarkable plasticity invasive trophoblasts fulfil numerous functions, i.e. anchorage of the placenta, secretion of hormones, modulation of decidual angiogenesis/lymphangiogenesis and remodelling of maternal spiral arteries. The latter is required to increase blood flow to the placenta, thereby ensuring appropriate transfer of nutrients and oxygen to the developing fetus. Since failures in vascular changes of the placental bed are associated with pregnancy diseases such as preeclampsia or intrauterine growth restriction, basic research in this particular field focuses on molecular mechanisms controlling trophoblast invasion under physiological and pathological conditions. Throughout the years, an increasing number of growth factors, cytokines and angiogenic molecules controlling trophoblast motility have been identified. These factors are secreted from numerous cells such as trophoblast, maternal epithelial and stromal cells, as well as uterine NK cells and macrophages, suggesting that a complex network of cell types, mediators and signalling pathways regulates trophoblast invasiveness. Whereas essential features of the invasive trophoblast such as expression of critical proteases and adhesion molecules have been well characterised, the interplay between different cell types and growth factors and the cross-talk between distinct signalling cascades remain largely elusive. Similarly, key-regulatory transcription factors committing and differentiating invasive trophoblasts are mostly unknown. This review will summarise our current understanding of growth factors and signal transduction pathways regulating human trophoblast invasion/migration, as well as give insights into novel mechanisms involved in the particular differentiation process.

AKT controls human first trimester trophoblast cell sensitivity to FAS-mediated apoptosis by regulating XIAP expression

The PIK3/AKT pathway plays an important role in both the inhibition of the apoptotic cascade and the promotion of cell growth and proliferation. Multiple apoptosis-related targets of phosphatidylinositide 3-kinase (PIK3) and protein kinase B (AKT) have been identified, including the antiapoptotic protein XIAP. By phosphorylating XIAP, AKT was previously shown to prevent the ubiquitinization and degradation of XIAP. First-trimester trophoblast cells express high levels of XIAP, which protects them from certain apoptotic stimuli. In this study, we determine that the inhibition of the PIK3/AKT pathway induces XIAP inactivation and the activation of caspase 3 in first-trimester trophoblast cells. Using a specific AKT inhibitor and a XIAP mutant construct, which mimics the AKT phosphorylated form of XIAP, we also demonstrate that these effects are dependent on the phosphorylation of XIAP by AKT. Finally, we show that the selective inhibition of AKT renders normally resistant first-trimester trophoblast cells sensitive to FAS-mediated apoptosis by regulating XIAP expression. Our findings may provide a link between AKT, XIAP, and the regulation of the FAS apoptotic cascade in first-trimester trophoblast cells and contribute to our current knowledge of the molecular mechanisms mediating normal trophoblast physiology during pregnancy.

Differentiation-induced post-transcriptional control of B7-H1 in human trophoblast cells

Trophoblast expression of immunomodulatory proteins in the human placenta is among the mechanisms that are critical for ensuring lymphocyte tolerance to the semi-allogeneic fetus. High levels of B7-H1 on trophoblast cells together with the known role of this protein in establishment of peripheral tolerance suggest that B7-H1 mediates immunological protection of the placenta during gestation. In this study, we investigated the molecular mechanisms of regulation of B7-H1 in trophoblast cells by epidermal growth factor (EGF), a key regulator of trophoblast cell differentiation. EGF increased B7-H1 protein levels within 24 h and mRNA levels within 4h of the initiation of treatment; by 24 h B7-H1 mRNA levels were similar between control and EGF-treated cells. Analysis of two different potential promoter regions revealed strong promoter activity in response to IFN-gamma. In contrast, no promoter activity could be induced by EGF, suggesting that this cytokine regulates B7-H1 expression post-transcriptionally in trophoblast cells. EGF-induced B7-H1 protein expression was completely blocked in the presence of inhibitors of the PI3Kinase/Akt/mTOR pathway, a pathway known to regulate gene expression at the translational level. Finally, analysis of monosomal and polysomal mRNA fractions of untreated and EGF-treated term trophoblast cells revealed that EGF induces a shift towards the translatable fractions and away from the untranslated fractions. These results highlight a novel mechanism for regulation of B7 family proteins in the placenta.

AKT induces senescence in primary esophageal epithelial cells but is permissive for differentiation as revealed in organotypic culture

Epidermal growth factor receptor (EGFR) overexpression and activation is critical in the initiation and progression of cancers, especially those of epithelial origin. EGFR activation is associated with the induction of divergent signal transduction pathways and a gamut of cellular processes; however, the cell-type and tissue-type specificity conferred by certain pathways remains to be elucidated. In the context of the esophageal epithelium, a prototype stratified squamous epithelium, EGFR overexpression is relevant in the earliest events of carcinogenesis as modeled in a three-dimensional organotypic culture system. We demonstrate that the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway, and not the MEK/MAPK (mitogen-activated protein kinase) pathway, is preferentially activated in EGFR-mediated esophageal epithelial hyperplasia, a premalignant lesion. The hyperplasia was abolished with direct inhibition of PI3K and of AKT but not with inhibition of the MAPK pathway. With the introduction of an inducible AKT vector in both primary and immortalized esophageal epithelial cells, we find that AKT overexpression and activation is permissive for complete epithelial formation in organotypic culture, but imposes a growth constraint in cells grown in monolayer. In organotypic culture, AKT mediates changes related to cell shape and size with an expansion of the differentiated compartment.

Differentiation of trophoblast giant cells and their metabolic functions are dependent on peroxisome proliferator-activated receptor beta/delta

Mutation of the nuclear receptor peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta) severely affects placenta development, leading to embryonic death at embryonic day 9.5 (E9.5) to E10.5 of most, but not all, PPARbeta/delta-null mutant embryos. While very little is known at present about the pathway governed by PPARbeta/delta in the developing placenta, this paper demonstrates that the main alteration of the placenta of PPARbeta/delta-null embryos is found in the giant cell layer. PPARbeta/delta activity is in fact essential for the differentiation of the Rcho-1 cells in giant cells, as shown by the severe inhibition of differentiation once PPARbeta/delta is silenced. Conversely, exposure of Rcho-1 cells to a PPARbeta/delta agonist triggers a massive differentiation via increased expression of 3-phosphoinositide-dependent kinase 1 and integrin-linked kinase and subsequent phosphorylation of Akt. The links between PPARbeta/delta activity in giant cells and its role on Akt activity are further strengthened by the remarkable pattern of phospho-Akt expression in vivo at E9.5, specifically in the nucleus of the giant cells. In addition to this phosphatidylinositol 3-kinase/Akt main pathway, PPARbeta/delta also induced giant cell differentiation via increased expression of I-mfa, an inhibitor of Mash-2 activity. Finally, giant cell differentiation at E9.5 is accompanied by a PPARbeta/delta-dependent accumulation of lipid droplets and an increased expression of the adipose differentiation-related protein (also called adipophilin), which may participate to lipid metabolism and/or steroidogenesis. Altogether, this important role of PPARbeta/delta in placenta development and giant cell differentiation should be considered when contemplating the potency of PPARbeta/delta agonist as therapeutic agents of broad application.

Modulation of trophoblast stem cell and giant cell phenotypes: analyses using the Rcho-1 cell model

Trophoblast giant cells are located at the maternal-embryonic interface and have fundamental roles in the invasive and endocrine phenotypes of the rodent placenta. In this report, we describe the experimental modulation of trophoblast stem cell and trophoblast giant cell phenotypes using the Rcho-1 trophoblast cell model. Rcho-1 trophoblast cells can be manipulated to proliferate or differentiate into trophoblast giant cells. Differentiated Rcho-1 trophoblast cells are invasive and possess an endocrine phenotype, including the production of members of the prolactin (PRL) family. Dimethyl sulfoxide (DMSO), a known differentiation-inducing agent, was found to possess profound effects on the in vitro development of trophoblast cells. Exposure to DMSO, at non-toxic concentrations, inhibited trophoblast giant cell differentiation in a dose-dependent manner. These concentrations of DMSO did not significantly affect trophoblast cell proliferation or survival. Trophoblast cells exposed to DMSO exhibited an altered morphology; they were clustered in tightly packed colonies. Trophoblast giant cell formation was disrupted, as was the expression of members of the PRL gene family. The effects of DMSO were reversible. Removal of DMSO resulted in the formation of trophoblast giant cells and expression of the PRL gene family. The phenotype of the DMSO-treated cells was further determined by examining the expression of a battery of genes characteristic of trophoblast stem cells and differentiated trophoblast cell lineages. DMSO treatment had a striking stimulatory effect on eomesodermin expression and a reciprocal inhibitory effect on Hand1 expression. In summary, DMSO reversibly inhibits trophoblast differentiation and induces a quiescent state, which mimics some but not all aspects of the trophoblast stem cell phenotype.

Molecular mechanisms of trophoblast survival: From implantation to birth

Fetal development depends upon a coordinated series of events in both the embryo and in the supporting placenta. The initial event in placentation is appropriate lineage allocation of stem cells followed by the formation of a spheroidal trophoblastic shell surrounding the embryo, facilitating implantation into the uterine stroma and exclusion of oxygenated maternal blood. In mammals, cellular proliferation, differentiation, and death accompany early placental development. Programmed cell death is a critical driving force behind organ sculpturing and eliminating abnormal, misplaced, nonfunctional, or harmful cells in the embryo proper, although very little is known about its physiological function during placental development. This review summarizes current knowledge of the cell death patterns and molecular pathways governing the survival of cells within the blastocyst, with a focus on the trophoblast lineage prior to and after implantation. Particular emphasis is given to human placental development in the context of normal and pathological conditions. As molecular pathways in humans are poorly elucidated, we have also included an overview of pertinent genetic animal models displaying defects in trophoblast survival.

The PI3K/Akt pathway is present and functional in the preimplantation mouse embryo

The PI3K/Akt signal transduction pathway is a well-known mediator of growth promoting and cell survival signals. While the expression and function of this pathway have been documented during early and late stages of the reproductive process, currently, there is no evidence demonstrating either the presence or function of the PI3K/Akt pathway in murine preimplantation embryos. We found, using confocal immunofluorescent microscopy and Western blot analysis, that the p 85 and p110 subunits of PI3K and Akt are expressed from the 1-cell through the blastocyst stage of murine preimplantation embryo development. These proteins were localized predominantly at the cell surface from the 1-cell through the morula stage. At a blastocyst stage, both PI3K and Akt exhibited an apical staining pattern in the trophectoderm cells. Interestingly, phosphorylated Akt was detected throughout murine preimplantation development, and its presence at the plasma membrane is a reflection of its activation status. Inhibition of Akt activity had significant effects on the normal physiology of the blastocyst. Specifically, inhibition of this pathway resulted in a reduction in insulin-stimulated glucose uptake. In addition, inhibiting Akt activity resulted in a significant delay in blastocyst hatching, a developmental step facilitating implantation. Finally, we established the presence of this pathway in trophoblast stem (TS) cells, a potentially useful in vitro model to study this signaling cascade. Taken together, these data are the first to demonstrate the presence and function of the PI3K/Akt pathway in mammalian preimplantation embryos.

Sheep Endogenous Betaretroviruses (enJSRVs) and the Hyaluronidase 2 (HYAL2) Receptor in the Ovine Uterus and Conceptus

The ovine genome contains approximately 20 copies of endogenous betaretroviruses (enJSRVs) that are highly related to two exogenous oncogenic viruses, Jaagsiekte sheep retrovirus (JSRV) and Enzootic nasal tumor virus. The cellular receptor for both JSRV and the enJSRVs is hyaluronidase 2 (HYAL2). In this study, we assessed expression of enJSRVs envelope (env) and HYAL2 mRNAs in the ovine uterus and conceptus (embryo/fetus and extraembryonic membranes) throughout gestation. By reverse transcription-polymerase chain reaction analyses, enJSRVs env were found to be expressed beginning in the Day 12 conceptus, whereas HYAL2 was expressed from Day 16. HYAL2 mRNA was detected throughout gestation in the placentome but not in the endometrium, whereas enJSRVs env expression was detected throughout gestation in endometrium and placentomes. The enJSRVs env mRNA was specifically expressed in the endometrial lumenal epithelium (LE) and glandular epithelium (GE) as well as the trophoblast giant binucleate cells (BNC) and multinucleated syncytia of the placenta. HYAL2 mRNA was only detected in the BNC and multinucleated syncytial plaques of the placentome. Partial sequencing of the transcriptionally active enJSRVs from sheep endometrium, placentomes, and placenta revealed expression of many enJSRV loci. Cloning of the expressed enJSRVs env mRNA from ovine uteroplacental tissues found sequences similar to the previously identified enJS5F16 and enJS56A1 gene with an intact open reading frame, although the polypeptides they encode were not studied. Collectively, results provide further support for our hypothesis that the enJSRVs Env have been beneficial to the host and are involved in protection of the uterus from viral infection and regulators of placental morphogenesis and function.

Maternal segregation of the Dutch preeclampsia locus at 10q22 with a new member of the winged helix gene family

Preeclampsia is a pregnancy-associated disease with maternal symptoms but placental origin. Epigenetic inheritance is involved in some populations. By sequence analysis of 17 genes in the 10q22 region with maternal effects, we narrowed the minimal critical region linked with preeclampsia in the Netherlands to 444 kb. All but one gene in this region, which lies within a female-specific recombination hotspot, encode DNA- or RNA-binding proteins. One gene, STOX1 (also called C10orf24), contained five different missense mutations, identical between affected sisters, cosegregating with the preeclamptic phenotype and following matrilineal inheritance. Four STOX1 transcripts are expressed in early placenta, including invasive extravillus trophoblast, generating three different isoforms. All contain a winged helix domain related to the forkhead (FOX) family. The largest STOX1 isoform has exclusive nuclear or cytoplasmic expression, indicating activation and inactivation, respectively, of the PI3K-Akt-FOX pathway. Because all 38 FOX proteins and all 8 STOX1 homologs have either tyrosine or phenylalanine at position 153, the predominant Y153H variation is highly mutagenic by conservation criteria but subject to incomplete penetrance. STOX1 is a candidate for preeclampsia controlling polyploidization of extravillus trophoblast.

G-CSF-induced tyrosine phosphorylation of Gab2 is Lyn kinase dependent and associated with enhanced Akt and differentiative, not proliferative, responses

The granulocyte colony-stimulating factor receptor (G-CSFR) transduces intracellular signals for myeloid cell proliferation, survival, and differentiation through the recruitment of nonreceptor protein tyrosine kinases Lyn and janus kinase 2 (Jak2). This results in the tyrosine phosphorylation of a small set of positive and negative adapters and effectors. Grb2-associated binder-2 (Gab2) is a newly described adapter molecule, preferentially expressed in hematopoietic cells and associated with phosphatidylinositol 3 (PI3) kinase. Studies suggest that Gab2 plays both positive and negative roles in cytokine receptor signaling. To investigate the role Gab2 plays in G-CSF receptor-mediated signaling, we have analyzed its activation state and correlated that with wild-type and mutant G-CSF receptors stably expressed in the murine factor-dependent Ba/F3 cell lines. G-CSF-induced tyrosine phosphorylation of Gab2 occurred in the wild-type and single Y-to-F mutants (Y704F, Y729F, and Y744F), but not in the ADA and W650R loss-of-function mutants. Cells expressing truncated proximal G-CSFR, the tyrosine-null (Y4F) G-CSFR, or Y764F mutant receptors had decreased phosphorylation of Gab2. Specific inhibitors of Src kinase (PD173 and PP1) but not Jak2 kinase (AG490) blocked Gab2 phosphorylation. Phosphorylation of Gab2 occurred in wild-type, but not Lyn-deficient, G-CSFR-transfected DT40 B cells. These data propose that Lyn, not Jak2, phosphorylates Gab2 and that maximal phosphorylation of Gab2 requires Y764, a Grb2-binding site. Serine phosphorylation of Akt, a marker of PI3-kinase activity, was detected in both wild-type and truncated proximal domain receptors, but not in the ADA and W650R mutants. Levels of phospho-Akt and phospho-extracellular signal-regulated kinase (phospho-ERK) were greater in proximal truncated than in wild-type G-CSFR cells, suggesting that Gab2 is dissociated from PI3 kinase or ERK activities. Overexpression of Gab2 enhanced the phosphorylation state of Akt, but not of ERK. This inhibited the proliferation of wild-type and truncated G-CSFR-transfected Ba/F3 cells and enhanced their myeloid differentiation. All together, these data indicate that G-CSF treatment leads to Lyn-mediated tyrosine phosphorylation of Gab2, which may serve as an important intermediate of enhanced Akt activity and myeloid differentiation, not growth/survival response.

Protein kinase B alpha/Akt1 regulates placental development and fetal growth

Protein kinase B alpha (PKB alpha/Akt1) is implicated in the regulation of metabolism, transcription, cell survival, angiogenesis, cell migration, growth, and tumorigenesis. Previously, it was reported that PKB alpha-deficient mice are small with increased neonatal mortality (Cho, H., Thorvaldsen, J. L., Chu, Q., Feng, F., and Birnbaum, M. J. (2001) J. Biol. Chem. 276, 38349-38352 and Chen, W. S., Xu, P. Z., Gottlob, K., Chen, M. L., Sokol, K., Shiyanova, T., Roninson, I., Wenig, W., Suzuki, R., Tobe, K., Kadowaki, T., and Hay, N. (2001) Genes Dev. 15, 2203-2208). Here we show that PKB alpha is widely expressed in placenta including all types of trophoblast and vascular endothelial cells. Pkb alpha-/- placentae display significant hypotrophy, with marked reduction of the decidual basalis and nearly complete loss of glycogen-containing cells in the spongiotrophoblast, and exhibit decreased vascularization. Pkb alpha-/- placentae also show significant reduction of phosphorylation of PKB and endothelial nitric-oxide synthase. These defects may cause placental insufficiency, fetal growth impairment, and neonatal mortality. These data represent the first evidence for the role of PKB alpha and endothelial nitricoxide synthase in regulating placental development and provide an animal model for intrauterine growth retardation.